Preimplantation genetic diagnosis (PGD) is a specialized procedure that screens embryos for specific genetic conditions before implantation. This advanced technique allows for the selection of embryos less likely to carry inherited disorders. PGD is typically used with in vitro fertilization, providing families with more informed reproductive choices.
Foundational Scientific Discoveries
PGD’s development relied on earlier scientific breakthroughs in reproductive biology and genetic analysis. A significant precursor was in vitro fertilization (IVF) technology, which allows eggs to be fertilized outside the body. The first successful human birth through IVF occurred in 1978 in the United Kingdom. This provided the means to access and manipulate early-stage human embryos for diagnostic purposes.
Parallel to IVF, genetic analysis techniques also progressed. Direct genetic analysis began in the 1950s, identifying chromosomal abnormalities like Down syndrome through karyotyping. The 1985 development of polymerase chain reaction (PCR) enabled amplification of tiny DNA amounts for detailed genetic testing. These combined advancements created the scientific environment for PGD to emerge.
Pioneering Moments in PGD
The first successful application of PGD occurred in the late 1980s. In 1989, British embryologist Alan Handyside and colleagues first used PGD to test for genetic defects in embryos. The first live births following PGD procedures were reported in 1990.
During early procedures, one or two blastomeres were carefully removed from a three-day-old embryo. This process, known as embryo biopsy, was performed without damaging the remaining embryonic cells. Genetic material from these biopsied cells was analyzed using techniques like PCR for gene mutations or FISH for chromosomal abnormalities. This pre-implantation testing offered families a way to avoid transmitting serious inherited genetic diseases.
Evolution and Accessibility
PGD technology continued to evolve, leading to improved techniques and broader applications. Early embryo biopsy methods, such as cleavage-stage biopsy, were refined. Newer approaches, like trophectoderm biopsy on day five or six blastocysts, became more common. This later-stage biopsy removes cells from the outer layer, which forms the placenta, leaving the inner cell mass undisturbed.
Advancements in genetic analysis expanded PGD’s capabilities. Techniques like array comparative genomic hybridization (aCGH) and next-generation sequencing (NGS) allow comprehensive screening of all 24 chromosomes for aneuploidies and a wider range of single-gene disorders. These improvements enhanced PGD’s accuracy and reliability, making it possible to screen for conditions like Tay-Sachs disease, sickle cell anemia, and chromosomal rearrangements. This increased precision and expanded scope made PGD more accessible to couples seeking to reduce the risk of passing on inherited conditions.